In telecommunications networks, the vehicle that is used for offering a wide range of different services, such as data, voice and video services, is often based on Asynchronous Transfer Mode (ATM) protocols. These protocols define a particular data structure referred to as a cell, which is a data packet of a fixed size. A cell typically comprises 53 octets, each octet comprising eight bits, and is formed by a five-octet header for transporting routing and user information and a 48-octet payload.
Referring to FIG. 1 an industry standard configuration of an Integrated Digital Loop Carrier (IDLC) is illustrated generally by numeral 100. The IDLC comprises an Integrated Digital Terminal (IDT) 102 located at or near a central office (CO) and a Remote Digital Terminal (RDT) 104 located at or near a customer neighbourhood. The IDT 102 is coupled to a Public Switched Telephone Network (PSTN) 105. The IDT 102 is further coupled to the RDT 104 via a high-speed digital circuit 106 such as a T1 or E1, or even higher speed interfaces such as on Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH). The RDT 104 is further coupled to a plurality of customer loops 108.
Media traffic between the customer loops 108 and the PSTN network 105 is collated by the RDT 104 and multiplexed over the high-speed circuit 106 to the IDT 102. In some configurations, the RDT 104 supports several high-speed circuits 106, with each high-speed circuit 106 coupled with a different IDT 102.
The RDT is an intelligent network element that interfaces between customer access lines and Time Division Multiplexing (TDM) facilities. The RDT 104 comprises a Host Digital Terminal (HDT) 110 and a Remote Terminal (RT) 112. The HDT 110 aggregates traffic from one or more RTs, and terminates interfaces to the TDM facilities, which interface to the PSTN. The RT connects to the customer loops and aggregates the analog signals by multiplexing them into a Digital Transport Facility 114, which supports TDM, Asynchronous Transport Mode (ATM), Internet Protocol (IP) bearer path and the like. A Broadband Loop Carrier (BLC) is an evolving access device providing these functions. BLCs plus other access devices, such as Digital Loop Carriers (DLCs), Digital Subscriber Loop Access Multiplexers (DSLAMs), plus other multi-service equipment, have evolved to provide customer line interface equipment that interfaces both TDM traffic and packetized traffic with the customer loops 108. For example, various Digital Subscriber Line (DSL) technologies provide this functionality.
Primarily, telecommunication access devices have been implemented using TDM as the Digital Transport technology of choice. TDM technology divides the available bandwidth into timeslots and assigns a predefined timeslot to each subscriber line. The subscriber line transmits its data to the network during its assigned timeslot. As such, existing access devices normally provide a TDM interface to the network in the form of T1 or T3 carrier links. As the amount of data traffic travelling over public packet networks outgrows voice traffic, new access devices 116 have become available which provide connectivity to next-generation packet networks, thereby enabling call services to be provided over a packet network 117.
To promote high-speed information transmission, the TDM-based access devices and networks which have already been deployed would have to be replaced with, or augmented with ATM-based access devices and ATM networks, which requires an immense expense. Accordingly, it has been suggested that the TDM network and the ATM network have to be utilized side by side. However, this method requires maintenance of two systems, which can lead to an excessive number of interfaces required for new equipment.
One method of reducing the number of system interfaces (physical buses and/or data links) within both the access device and the network is to use only one protocol for data and voice transfer. This requires that all data flows that are not already in the format of a selected protocol must be encapsulated into the format of the selected protocol before transfer over the system interfaces. It also requires that flows must be recovered from the format of the selected protocol before being processed in their native format.
Thus, there is a need for systems that can efficiently transfer and cross-connect TDM voice flows within standalone nodes such as access devices, or distributed systems linking various nodes across a telecommunications network. It is an object of the present invention to obviate or mitigate at least some of the above-mentioned disadvantages.